<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        body>div {
            width: 200px;
            /*height: 200px;*/
            border: 1px solid red;
            /* 当元素的所有子元素全部浮动时,自动识别的高度为0
               后面的元素会顶上来导致显示异常,添加overflow: hidden解决异常 */
            overflow: hidden;
        }
        #d1 {
            width: 50px;
            height: 50px;
            background-color: red;
            float: left;
        }
        #d2 {
            width: 50px;
            height: 50px;
            background-color: green;
            float: left;
        }
        #d3 {
            width: 50px;
            height: 50px;
            background-color: blue;
            float: left;
        }
    </style>
</head>
<body>
    <div>
        <div id="d1"></div>
        <div id="d2"></div>
        <div id="d3"></div>
    </div>
    <div>div</div>
</body>
</html>